The present invention relates to a pulse motor driving circuit and, more particularly to an improved pulse motor circuit for driving a floppy disc of the four-phase bipolar type to stably move a head by reducing heat radiation.
In recent years, floppy disc devices each having a head and a pulse motor for driving the head have been developed and are widely used as external storage device for storing data or information from a computer, a personal computer or a word processor, or the like.
Generally, to reduce the power consumption of the pulse motor in order to control heat radiation, two powers +5 V and +12 V outputted from external power sources are applied to internal circuits including the pulse motor. For example, while the head of the floppy disc device is moved, 12 V power is applied to the pulse motor for driving the head. After the movement of the head is completed, the pulse motor driving voltage is changed from 12 V to 5 V so as to dispose the head at the waiting position while waiting for the next movement.
In case where a single power source of +5 V is used as a device for supplying into the internal circuits of the floppy disc so as to simplify the power source, the following methods are used for reducing the driving voltage for the pulse motor while the head is disposed at the waiting position while waiting for the next movement:
(1) An effective driving voltage for the pulse motor is reduced by a chopper control while the head is at the waiting position waiting for the next movement.
(2) A low voltage for driving the head while at the waiting position for the next movement is applied by switching the external 5 V power source, using controls inside the floppy disc device, so that the pulse motor driving voltage is reduced similar to using the two power sources in the conventional manner.
(3) The power from the external voltage source is applied to the driving circuit for the pulse motor via a resistance while the head is at the waiting position for the next movement, so that the driving voltage for the pulse motor is reduced by a voltage drop of the resistance.
In the methods (1) and (2), it may happen that the floppy disc is deteriorated because a noise, caused by switching, damages a head reproducing system. In method (3), it may happen that the resistance radiates an excess heat.